Alert Notice 630: Coverage needed TONIGHT for ASASSN-18ey = MAXI J1820+070

April 11, 2018: Dr. Gregory Sivakoff (University of Alberta), on behalf of a large number of collaborators, has requested AAVSO observers' assistance in monitoring the outbursting black hole X-ray binary ASASSN-18ey = MAXI J1820+070 in support of a multiwavelength "blitz" campaign taking place tonight and into tomorrow.

Dr. Sivakoff writes: "Black hole X-ray binaries tend to undergo one of two types of outbursts. The first (often called a "canonical outburst") involves a variety of changes in the properties of the disk that feeds the black hole and the jets/winds that can escape before they fall within the black hole's event horizon. The second (often called a "hard-state-only outburst") only involves the "hard" and the "hard-intermediate" accretion states. Each outburst provides different opportunities for studying the connection between accretion inflows and outflows.

"MAXI J1820+070/ASASSN-18ey (hereafter MAXI J1820+070 to save a few characters) has appeared to have stalled its evolution in the "hard" state. This behaviour tends to occur in "hard-state-only" outbursts. For observers, the stalled behaviour means an extended opportunity to study the "hard" accretion state (which has an analogue with the accretion state of the vast majority of accreting supermassive black holes). While many of our observational programs were hoping to catch that transition from the "hard" state through the "intermediate" states to the "soft" state, we have adapted our plans to this outburst's behaviour. (And to be fair, many observational programs were already designed for the "hard" state).

"A second implication of the stalled behaviour at its current bright levels is that MAXI J1820+070 may be atypically close for a black hole X-ray binary. I have estimated that the source could be only 1 kpc (3260 light-years) away, which would make it one of the nearest black hole X-ray binaries. This possibility has many of us quite excited; GAIA should provide the distance measurement via parallax soon."

He continues: "I am leading what I like to call a "blitz" campaign on the source. I use this term for a significant multiwavelength campaign focussed on a single day. My collaborators and I have planned this blitz for the night of April 11th. (Again I apologize for the short delay, but putting this together has taken all of my time recently). The campaign is designed to measure both rapid variability features (0.01 - 100 Hz) from X-ray to radio frequencies and the (quasi-)simultaneous broad-band spectral energy distribution. Since the campaign is focusing on facilities that can see MAXI J1820+070 at some time within the window of April 12th 05:00 - 15:00 UTC, we strongly encourage multiwavelength observations (and communication of those observations) within that window. Observations within approximately 24 hours on either side of the window will also be useful for this campaign.

"For those with the capacity to do many high cadence CCD/CMOS observations on this bright source, we have been using the following comparison star:  URAT1 486-270264 (Zacharias et al. 2015) at RA=18h20m26.43s, Dec=+07d10m11.8s. For an example, see . [Note: In the photometry table for the AAVSO sequence for ASASSN-18ey, the URAT1 star has the AUID 000-BMQ-477.]

"I have reports that 1 Hz (1-second exposure) imaging can be done on a 12" telescope with a fairly standard CCD. Although I cannot verify what the readout time or the what type of shutter was used. If you are going to try high cadence observations, be aware that both readout time and your shutter may be a limiting factor. Some detectors are capable of sub-array modes that reduce readout time at the sacrifice of your field of view."

Beginning now and continuing through 2018 April 13, V time series are requested, with as short a cadence as possible (ideally, a time resolution of 0.1 second or better). If doing high-cadence time series, please see above regarding the comp star to use.

Please see AAVSO Alert Notice 624 for more information about this object.

ASASSN-18ey = MAXI J1820+070 has a published optical range of 12.5 CV - 18.3: V. The most recent observations submitted to the AAVSO International Database are:
 2018 Apr. 11.38536 UT, 12.249 CV +/-0.008 (F.-J. Hambsch, Mol, Belgium);
11.38548, 12.302 CV +/-0.008 (Hambsch);
11.38561, 12.384 CV +/-0.008 (Hambsch);
11.38572, 12.248 CV +/-0.009 (Hambsch);
11.38584, 12.190 CV +/-0.008 (Hambsch);
11.38597, 12.226 CV +/-0.008 (Hambsch);
11.38608, 12.375 CV +/-0.009 (Hambsch);

Coordinates (2000.0):  R.A. 18 20 21.95   Dec. +07 11 07.3

Charts with a comparison star sequence for ASASSN-18ey may be created using the AAVSO Variable Star Plotter (VSP). You may use either ASASSN-18ey or MAXI J1820+070 as the name when creating a chart. Note the comment above regarding choice of comparison star if carrying high-cadence time series observations.

Please submit observations to the AAVSO International Database using the name ASASSN-18ey.

This observing campaign is being followed on the AAVSO Time Sensitive Alerts online forum at

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.

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